As the Sun is incompatible with Saturn, Venus, Rahu and Ketu, Sun gems such as ruby should not be used with blue sapphire, diamond, hessonite or cat's eye.

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As the Moon is incompatible with Rahu and Ketu, Moon gems such as pearl should not be used with hessonite or cat's-eye. 

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As Jupiter is incompatible with Mercury and Venus, Jupiter gems such as yellow sapphire should not be used with emerald or diamond.

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As Rahu (Moon’s north node) is incompatible with Sun and Moon, Rahu gems such as hessonite should not be used with ruby or pearl.

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As Mercury is incompatible with the Moon, Mercury gems such as emerald should not be used with pearl or moonstone.

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As Venus is incompatible with the Sun and Moon, diamonds and other colorless gems should not be used with rubies or pearls.

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As Ketu (Moon’s south node) is incompatible with Sun and Moon, cat's eye gems should not be used with rubies or pearls.

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As Saturn is incompatible with Sun, Moon and Mars, Saturn gems such as blue sapphire should not be used with ruby, pearl or red coral.

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As Mars is incompatible with Mercury and Saturn , Mars gems like red coral should not be used with emerald or blue sapphires.

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Ref. ©1995 Ancient Astrological Gemstones & Talismans